The forwardAsRawChatCompletions path (used when APIKey accounts target
upstreams that don't support Responses API, e.g. DeepSeek) was missing
reasoning_effort and service_tier extraction, causing all reasoning
effort values to be silently dropped.
Extract both from the raw Chat Completions body before forwarding, and
propagate them through streamRawChatCompletions / bufferRawChatCompletions
to the OpenAIForwardResult.